The Formation of Acetyl Co-enzyme A
A large number of molecules that are synthesised in cells are built from two-carbon acetyl groups. An acetyl group derives from ethanoate (acetate) and is named acetyl when it forms a group within a larger molecule. Instead of using free acetate molecules the cell 'activates' the molecule by attaching it to Coenzyme A (CoA).
The acetyl group can derive from pyruvate (and ultimately from monosaccharides if that is the main 'food' for the cell). The two processes of oxidising/decarboxylating pyruvate and attaching the resulting acetyl group to CoA are coupled.
Oxidative decarboxylation is catalyzed by the pyruvate dehydrogenase complex. It is a multimeric assembly of three kinds of enzyme that implements the process in four steps. The animation shows all four steps in sequence and data sheets follow.